1. Field of Invention
The invention relates to a four-stroke internal combustion engine (ICE) and more particularly to an improved lubrication system for a small lightweight four-stroke engine.
2. Description of Related Art
Portable power tools such as lawn movers, line trimmers, chain saws were mostly powered by two-stroke ICEs in earlier days. Gradually, two-stroke engines were phased out due to heavy harmful exhaust emissions (e.g., hydrocarbon (HC)). Nowadays, almost all such portable power tools are powered by four-stroke ICEs.
Lubrication becomes a very serious problem since portable power tools are required to operate in a wide range of orientations (i.e., being tilted or even upside down). There have been numerous suggestions in prior patents for solving this problem. For example, U.S. Pat. No. 7,287,508 discloses an engine lubrication method which is incorporated herein by reference. Thus, continuing improvements in the exploitation of lubrication system for a small lightweight four-stroke engine are constantly being sought.